Barometric Pressure

[Rick Thibert]

I am beginning to take notes on spawns coinciding with Barometric Pressure lows.

Does anyone know if it is at all a factor with cichlid behaviour?

BC

[Darrell Ullisch]

I have tons of anecdotal evidence of it, but haven't heard of any hard data. It is logical, as the lateral line sensitivity of fish in general makes it very possible for them to detect changes in barometric pressure. Corydoras are well known to react to low pressure passing through, and some Killifish will also increase production 10 fold under such conditions. I've seen almost every fish in my fishroom try to spawn at the same time when a record low went through some years ago; this included Pike Cichlids of the lepidota types, Red Hump Geophagus, Cyrtocara moori, and Gold form Etroplus maculatus. I believe there were almost 20 species of Killies, Tetras, Barbs, Gobies, and Cichlids, all at the same time. Most weren't all that ready to spawn, but they did lay eggs. Oddly, the livebearers didn't seem to be as affected, possibly because their reproductive methods aren't as tied to the ebb and flow of the water.

[Rick Thibert]

A bit of data I've been collecting:
http://www.oddballexpress.co.uk/phpBB2/ ... .php?t=709

BC

[Juan Artigas]

Just a thought, isn't it one atmosphere of barometric preassure equivalent to ten meters of water column? The lateral line is subject to a combination of both preassures then, atmosphere + water column. Now, a strong change in barometric preassure lets say a decrease in preassure (caused by an increase in moisture content in the air) sufficient enough to cause a storm must be around a tenth of an atmosphere, that is, a meter up in the water column. If a fish moves in the water column a meter up or down, that is enough to change the preassure on its lateral line to simulate the change in atmospheric preassure to predict a storm. For fish that regularly moves in the water column more than one meter, it would then be insignificant to experience an atmospheric preassure change enough to cause a storm. For fish limited in the water column or living in very shallow water like Corydoras or the weather loach it may not be the case though, but probably most cichlids will give damn about it.

[Bas Pels]

1 atm = 10 meters watercolomn, Juan is right. And his assumption about a storm beiing preceded by 1/10th is a bold one, 1/20th is enough for a normal storm, generally that is (hurricanes are in another league)

Still, these changes can for fish can be insignificant (50 cm), but it might be worth noting them - for fish which breed in the rainy season.

Therefore, the insignifacance of the change in barometric pressure as the fish experiences will, most likely, not be that important.

As far as I know, cichlids generally do not breed seasonwise. Some cichlids breed not all year, but only after a rich period, when the are fattend up. Other (such as Australoheros in their southern range) breed in spring - it makes sens not to breed in autumn, but on the other hand I still managed to have eggs in autumn.

So, I agree with Juan barometric pressure will not be that important for cichlids, but my fishes from southern South Americ are in a low temp / short days - high temp / long days cyclus, as I'm certaiin this will have an influence

[Darrell Ullisch]

On whether or not fish can detect a major change in atmospheric pressure: First, while fish can move up and down in the water column, if you observe for a while you will see that they really don't make large moves vertically all that often. They know what depth they are at, I would think, and instinctively know what it should feel like. Second, whether or not they can detect what you consider a minor change in the pressure really depends on the sensitivity of the lateral line, and my understanding is that it is quite sensitive in virtually all fishes. How much pressure is produced by a small fish moving one or two metres away? Yet fish can detect that movement, according to the behavior of predatory species. Fish use the detection of pressure the way we use hearing because of the nature of the environment in which they live. Water transmits such vibrations - and a vibration is nothing but a pressure wave - better than air, but the organ still has to be sensitive enough to detect relatively small changes.

On whether or not non-seasonal spawners will react to atmospheric pressure changes: it may be questionable whether or not most Cichlids breed seasonally, but it is a virtual certainty that rain is a signal of coming food increases. Nutrients washed into the water from the land often results in blossoms of various small creatures that fry feed on. And I do know that some West African Riverine species, such as Steatocranus casuarius, respond with spawning if there is an increase in the water movement, which happens after a rain. So it is reasonable to think that any fish that is reasonably close to condition would instinctively take such a signal - assuming that they can detect it - as an opportunity to reproduce at a time when their young will have the best chance of finding more than adequate food. I would especially think such a signal would be important to fish living in regions where such rains are infrequent.

I keep track of the barometer, for the simple reason that there are non-cichlid species I keep that absolutely do respond to such stimulus. The fact that I've observed various species of Cichlids spawning at the same time could be interpreted once, maybe twice, as coincidence; but the fact that it is observed not only by myself but others, repeatedly, when the only part of the weather they could possibly detect would be the atmospheric pressure, is hard to dismiss. If you are not in the habit of monitoring the barometer, you might think you just had an unusual incident with multiple pairs/species spawning close to the same time. Have you ever had one of those times? I've talked to people who have a bunch of fish spawn simultaneously, and they comment on it at a club meeting or some such. Because I track the data, I can usually tell them whether it corresponded to a LP front. Hasn't missed yet.

I do not have access to wild environments with cichlids, but I imagine if it were possible to take a census of how many pairs in a given area have eggs at the same time under normal conditions (maybe taken three or four times to get a reasonable average), and then take the same type of census within 48 hours of a major low pressure front passing through, it might produce some interesting data. Of course you would have to have some sort of weather monitoring station at the site to detect the front, and then signal the researcher. Not a cheap experiment, but I would not think totally impossible.

[Juan Artigas]

Although my cichlids regularly start spawning at home at the same time as Darrell points out, and as they do in the wild, I can not link the event to a barometric preassure change as my fish are subject to temperature changes (I don't keep them at a precise temperature with a thermostat all around the year) and also subject to natural light cycles (I don't keep them in a dark basement), so there are too many factors for me to link barometric preassure with breeding efforts. Having observed CA cichlids in their natural habitat for many years, I would be exceptikal that they know the depth they are in with high precission, they can not take a reference normaly as water levels are varying. On the contrary, I agree with Bas that the breeding stimuli has more to do with the proper conditions present (food, temperature, light, spawning area) than with any change in barometric preassure. Please note I am not saying this is the same case for all fish. The reasons why I think so are among others that cichlids breed all around the year, not paying attention to season, when the conditions are met, I put as example Herichtys minckleyi, H. bartoni and H. labridens (lacustrine) subject to similar conditions all around the year. More importantly, I often see riverine cichlids breed and then some days later an unexpected storm comes in and flushes away all eggs and fry. Why would they breed expending all that effort if they could predict the wheater? If they would, would it serve them? a sudden storm can not probably be predicted with barometric changes with many days of anticipation, so, what good would it do anyways?

[Bas Pels]

More importantly, I often see riverine cichlids breed and then some days later an unexpected storm comes in and flushes away all eggs and fry.

as far as I know, in Central America it is hard to predict the weather - the climate is mostly tropical, thus on average stable but exceptions do occur.

1 exception are hurricanes, but others might be more important. I heard many CA rivers are small, laying in deep deceptions, due to occasional watrerfalls - if it rains in the mountains, the river will rise, rapidly. So rain elsewhere is, in fact, more important than rain here. This will make it very hard for the fish to decide what to do: breed now, or wait a while.

A large part of Mexico is north America, less tropical, but quite often as stable as Central America

[Darrell Ullisch]

I was doing some research on the sensitivity of the lateral line. This is a most amazing organ. One paper on the ability of a Toadfish to detect prey had information from numerous references, including this one in particular:

Montgomery and Bodznick (1994) indicated that the lateral line medullary nuclei contain an adaptive filter capability that cancels input consistently associated with an animal's own movements.

In other words, the fish ignores normal movements related to itself. Any movement up or down the water column would be irrelevant to the ability to detect external changes in the environment because the fish is hardwired to filter out it's own movements. I find this to be almost unbelievably sophisticated in otherwise primitive life forms. Sort of like the ability of Jellyfish to pursue prey, which many didn't believe possible either - until it was proven by controlled experimentation.

I grew up seeing barometric pressure expressed as inches, rather than millibars, so bear with me. The average pressure in my region is around 30 inches, and normal variation can take it up or down .1 to .3 inches in a 24 hour period. Major lows producing a drop of .5 inches - or roughly a 1.5-2 % change - will result in spontaneous spawns from most small fish, such as Plant spawning Killifish, Corydoras Catfish, and Tetras. Note that most non-annual Killifish are also non-seasonal breeders, but a half inch drop in atmospheric pressure will regularly produce a ten fold increase in egg production in a 24 hour period. I have not observed a lot of Cichlids responding to these smaller, more common events. However, Apistogramma, Mikrogeophagus, and Pelvicachromis all have been observed to breed out of cycle on these occasions.

The incident in which I had 4 diverse species of Cichlid spawn, at the same time that about 15 other species of fish responded to a drop in pressure, was very unusual. A drop of over 1 inch occurred - very rare in this region, as we are far from the oceans - within a 12 hour period. That is a change of only about 3.5 %. But not only did I have a massive "fish Orgy", ALL the other large scale fish keepers in the local club also reported spawns from multiple species, including numerous Cichlids. Most of the cichlid keepers at that time had Malawian Mbuna and Haps, with a few Tanganikans. Whether or not any "Central American" species were involved I do not recall, other than my Geophagus steindachneri. The only spawn I ever got in two years of keeping a species of unidentified Goby occurred that night.

I'm not claiming that the fish wait for such an event to spawn. But there has to be some tactical advantage to breeding under those conditions that would cause them to evolve the response. I believe it is instinctual, as many of them were simply unable to resist; even fish that weren't ready were triggered by a change in pressure of less than 4 %. Temperature did not change, as I live in Snow Belt Michigan, and the temperature inside my home is kept quite constant because outside it can change a lot in a short time. Light? the drop occurred at night, most spawning shortly after the timed lights came on. No water changes immediately prior. No special feedings. The only detectable environmental change was the drop in the barometer.

Personally, I find it amusing when people try to tell me that something I've observed hundreds of times doesn't happen. I can tell you empirically that it happens; what I can't tell you is why, or exactly how much of a change is required to trigger a response, or even whether or not all species have the same response. Maybe deepwater species don't need to worry about it, I don't know. I can't afford a hyperbaric (sp?) chamber to do the necessary controlled experiments. I would be greatly interested in hearing about it if someone actually does try.

[James Shingler]

Do not assume that correlation means causation.

Two very different things.

To prove causation though would be easy. Mearly control the pressure to test your hypothysis.
Make the water a little less deap to lower the pressure.

Otherwise, no matter how much correlation evidence you gather (breeding with a natural drop in pressure)it is not evidence for causation (just correlation).

However if you could stimulate breeding by reducing the pressure (or depth) then you have evidence.

[Darrell Ullisch]

Reducing the water level does not bypass the instinctive data filter, see my reference in the previous post. The only way to test it would be to build a hyperbaric chamber, where one can control the actual atmospheric pressure. I can't even afford a trip to Atlanta this year, so such equipment is beyond my capability. However, if some one in the research community wanted to try it, I would imagine they can find grant money to help pay for such equipment, or at least the rental of such equipment.

[James Shingler]

"the instinctive data filter" Any evidence that this exists for external pressure ?

Sure, a fish is not fooled into sensing reduced pressure just by moving up in the water column (or by altering the depth of water in a tank maybe) but a simple water tower, and the top of the tank sealed would provide the low pressure changes required.
There is no reason why a fish should be adapted to filter out this pressure change as there is nothing like this in the wild.

No need for a barometric chamber capable of huge pressure changes.

As you say its sad to have "tons anecdotal evidence of it, but no hard data" or evidence.
Evidence that would help the skeptic scientist take the argument seriously. Species by species.

Whats interesting (for me) is not that some fish are able to detect and breed with changes in barometric pressure (thats common knowledge for many fish species) but which species of cichlid do this (and why).

And I guess how quickly they lose this ability when its not selected for (in fact selected against) in tank bred populations.